Kurta Corporation

Charles A Waterbury

James L Rodgers

James R Sciacero

Donald F Gray

A digitizing system includes a tablet and a cordless pointing device including a plurality of data grid conductors in the tablet and a plurality of clock grid conductors in the tablet, all receiving a magnetic field signal transmitted by the pointing device. A data channel circuit includes a differential amplifier and demodulating and filtering circuitry coupled to an output of the differential amplifier, having a clock input. An A/D converter has an input coupled to an output of the demodulating and filtering circuitry. Multiplexing circuitry selectively couples various grid conductor signals to the data channel circuit. A clock recovery circuit responsive to the clock grid conductors includes a phase-locked-loop circuit that generates a recovered clock signal which is synchronous with the magnetic field signal and is used as a reference for demodulating the phase and amplitude of signals multiplexed from the data grid conductors to the data channel circuit. Accurate determination of the pointer tip position is achieved simultaneously with accurate decoding of pointer commands represented by shifts in the frequency of the magnetic field signal.

Low power cordless magnetic field digitizer with differential grid

A digitizing system includes a differential noise reduction technique wherein spaced parallel grid conductors in a tablet are differentially sensed in order to cancel out locally induced noise signals. Grid conductors also are sensed in a single ended fashion to initially locate a grid conductor conducting a larger induced carrier signal amplitude than any other grid conductor and produce amplitude data that is used to eliminate ambiguities arising from differential sensing of pairs of spaced grid conductors.

Noise cancellation in digitizing system and method

A cordless pen emits a directional electric field from the tip of a conductive pen cartridge. The pen tip is capacitively coupled to embedded major X and major Y conductors in a digitizer tablet, which are scanned to determine which three X conductors and which three Y conductors have the greatest resulting signal levels. A microprocessor calculates the precise pen location from the three largest X signals and the three largest Y signals. A resistive path to ground is provided for each X and Y conductor. A plurality of minor conductors are disposed between each pair of X and Y conductors. A resistive divider circuit linearly distributes the voltage across the pair of conductors among the minor conductors therebetween, and improves the capacitively coupled signal levels and also 'localizes' noise signals. The frequency of the pen signal is modulated by several pen switches. Circuitry in the digitizing tablet discriminates the pen frequency to decode the commands represented by switch closures between data scanning operations. In one embodiment of the invention a keyboard is placed on the digitizer tablet. The keyboard includes a groud plane through which a plurality of conductive tips actuated by keys extend to capactively couple an electrical signal to embedded X and Y conductors. The microprocessor interprets the scanned data to determine the identity of each depressed key.

Growing community of inventors

Chandler, AZ, United States of America

Charles A Waterbury